Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity.
The workpiece is disposed on a platen while the ion beam is being directed toward the workpiece. The platen serves to hold the workpiece in place. In some embodiments, the platen also serves to remove any charge that collects on the surface of the workpiece during the implantation process. The presence of charge on the workpiece may adversely affect the implantation process. Additionally, the excess charge may make it difficult to remove the workpiece from the platen after the implantation process is completed.
In some embodiments, grounding structures, typically in the form of grounding pins, are used to remove this charge from the workpiece. These pins, which may be grounded, may have a sharp or tapered end that contacts the workpiece. Any charge collected on the workpiece passes through the tapered end and is dissipated.
However, it has been discovered that these grounding pins are not effective with all workpieces. For example, some workpieces have uncoated, or clean, back surfaces, other workpieces have one or more layers, which may be insulating layers, coating the back surfaces, and still other workpieces have back surfaces having additional differences. Different grounding configurations may be more effective for these different types of back surfaces.
Therefore, it would be advantageous if there were a platen that included a plurality of different types of grounding structures, where each type was most effective for a particular type of back surface. Furthermore, it would be beneficial if these different types could be readily employed based on the type of workpiece disposed on the platen.